These data originate from soil samples collected on several field campaigns, aiming at identifying impacts of large herbivore activity on soil carbon storage and degradation in permafrost (northeastern Siberia (68.51 °N, 161.50 °E); campaign in July 2019) and seasonally frozen Arctic ground (northern Finland (69.15 °N, 27.00 °E); campaigns in September 2020 and June 2022).
The samples were collected in transects across grazing intensity gradients, spanning over 5 different intensities:
1 - no grazing / exclosure sites (Siberia: 23 years; Finland: 50 years)
2 - occasional animal migration (Siberia: year-round; Finland: seasonal)
3 - daily animal migration (Siberia: year-round; Finland: seasonal)
4 - high-frequency daily animal migration (Siberia: year-round; Finland: seasonal)
5 - pasture / supplementary feeding sites (Siberia: year-round; Finland: seasonal)
Samples cover different ground types and seasonalities, which are marked out in the site names:
B - drained thermokarst basin
U - Yedoma upland
P - peat
M - mineral soil (podsol)
E - exclosure (Finland-specific)
S - reindeer summer ranges
W - reindeer winter ranges
In this context, 'grazing' refers to any animal activity exerted by large herbivorous animals, including browsing, trampling and defecation.
Values were measured following the lab procedure after Jongejans et al. (2021):
1. Lipids were extracted from the freeze-dried and homogenised samples using accelerated solvent extraction (ASE). For this, we used a ThermoFisher Scientific Dionex ASE 350, equipped with dichloromethane / methanol (DCM / MeOH 99:1 v/v) as the solvent. Samples were hold in a static phase for 20 minutes (heating for 5 minutes to 75 °C a 5 MPa). Extracts were subsequently concentrated using a Genevac SP Scientific Rocket Synergy evaporator at 42 °C.
2. Internal standards for compound quantification (5α-androstane for n-alkanes, 5α-androstan-17-one for n-alcohols) were added.
3. Asphaltenes (n-hexane-insoluble compounds) were removed by asphaltene precipitation.
4. The remaining maltene fraction was separated by medium pressure liquid chromatography (MPLC) (Radke et al. 1980) into aliphatic, aromatic and NSO (nitrogen-, sulphur- and oxygen-containing) compounds.
5. The NSO fraction was afterwards separated into acidic and neutral polar compounds applying column separation. The acidic compounds were trapped by impregnating the column with potassium hydroxide before sample addition. After washing the neutral compounds off the column using DCM, a mixture of DCM / formic acid (98:2 v/v) was added to wash the acidic compounds off the column.
6. The neutral NSO fraction, containing n-alcohols, was silyllated by adding 100 µl DCM / MSTFA (N-Methyl-N-(trimethylsilyl)trifluoroacetamide; 50:50 v/v) and heating for 60 minutes at 75 °C.
7. For measurement, we used a Thermo Scientific ISQ 7000 Single Quadrupole Mass Spectrometer with a Thermo Scientific Trace 1310 Gas Chromatograph (capillary column from BPX5, 2 mm x 50 m, 0.25 mm) with a MS transfer line temperature of 320 °C. The ion source temperature was set to 300 °C with an ionisation energy of 70 eV at 50 µA. The scan was set to the full mass spectrum (m/z 50-600 Da, 2.5 scans / second).
8. Peaks were identified and quantified in relation to the added standards using the software Xcalibur.
The measurement results of n-alkanes and n-alcohols are given in µg/g(TOC) in reference to the organic carbon (OC) content of the sediment samples.
